A typical way of accomplishing continued operation of an aircraft component, after failure of one operating mechanism is by the use of a quadruplexed system in which two sets of two signals are used. Each output signal representing a desired output position constitutes a channel of operation and the output signals of the two channels of one set of signals are mechanically compared by a balance beam arrangement. If the balance beam tips representing a disagreement between the two output position signals, a failure is indicated. There is no way to discriminate which of the two channels is not operating properly and, therefore, both channels must be considered to be in error and must be shut down or bypassed. Redundant operation can still occur, since this leaves the other set of two output signals operating as two channels still operating. The disadvantage of this quadruplexed system is that it is always necessary to shut down two channels of operation anytime a fault is indicated, which shuts down one-half of the system. Another consequence of this approach is that four sets of hardware are required, with resulting impact on cost as well as reliability and weight which are important factors in aircraft use.
The foregoing prior art does not disclose a system wherein three mechanical output signals of three separate channels can be compared to enable an improperly operating channel to be identified and shut down or bypassed. This leaves two operative channels with resulting improvement in system reliability, cost and weight over a quadruplexed system.
The Westbury et al. U.S. Pat. No. 3,411,410 discloses position control servo systems using a tripodal force-transmitting member rigidly connected to three actuating pistons for the member. Faulty operation of one of the actuating pistons is detected by sensing elements associated, one with each of the actuating pistons which are connected to three legs of a three-armed lever 14 constituting an averaging member and which is pivotally mounted at a central ball carried by a fixed reactor member. Faulty operation of one of the actuating pistons results in tipping movement of the three-armed lever 14, to result in differential movement of members associated therewith to indicate the actuating piston which is not operating properly. The three-armed lever is not connected into the system to be a force-transmitting member for transmitting the output position signals from the actuating pistons to an element to be positioned by the output signals.
The Stevko U.S. Pat. No. 3,762,237 discloses a digitally-controlled linear actuator having a tripodal summing device in the form of a spider assembly having three legs, each of which can receive an output position signal and transmit these signals to an output member pivotally connected to the spider assembly at a location interiorly of the three locations at which the output signals are applied and which define the apices of a triangle.
The prior art does not disclose a fault detector for a triplexed mechanical or hydromechanical system wherein: three output position signals in three separate channels are applied to a tripodal summing member pivotally connected to a force-transmitting member for positioning an operating device; the failure in one output position signal is evidenced by tipping of the tripodal summing member to give an indication as to which output position signal is incorrect; and through the use of appropriate detecting structure, the channel providing the deviant output position signal can either be shut down or bypassed and continued redundant operation is carried out by the remaining two channels each having an output position signal which is accurately delivered to the tripodal summing member.